There're a lot of issues: we're going to
cover the basics.
types of image files (vectoral/meta/object, bitmap)
GIF Graphics Interchange Format
GIF Anatomy of a GIF
Animated GIF, GIF 87a, 89a,interlacing and transparency
JPEG (Joint Photographic Experts Group)
Others--Quicktime, MPEG (Motion Pictures Experts Group), Shockwave, FutureSplash
GifBuilder (Mac),Gif Animator and others for PC, Gifsicle for Linux
For those of you trying to do animated gifs, try looking here
The Others -- Macromedia Director, Adobe Premiere, FutureSplash Animator
lossy and non-lossy
Delta animation techniques
Basic Photoshop tips
Size is not an advantage where web imagery is concerned: those of you who have large or inappropriately scaled images should try to rework them with Photoshop.
Some, icons could benefit from a change of format (gif->jpg)
Some animation (107k) could be made smaller with different configuration
of the GifBuilder (or other similar) software.
One can use the height=75 width=75 parameters of the IMG tag to force images down to the right scale, but this is not a good solution